1. Field of the Invention
The present invention relates to is directed to systems for detecting the presence of non-linear junctions such as are found in devices that contain semiconductors and more particularly to a detecting and locating system for use in revealing hidden RF receivers at a distance, particularly Improvised Explosive Devices (IED's).
2. Description of the Related Art
A variety of methods are presently being used for detonating IED's. These include command detonated devices; remote controlled devices such as battery powered doorbell devices, pagers, cell phones, etc.
Use of non-linear junction detectors (NLJD's) for detecting the presence of IED's is known. The operational principle of the non-linear junction detector (NLJD) is based on the effect of non-linear signal transudation inside objects containing semi-conducting components. Devices containing semi-conducting components react to high frequency signals transmitted by non-linear NLJD and re-radiate energy back on doubled and tripled frequencies of the original flooding signal. Electronic components return more second harmonic of the flooding signal and oxidized metal items and metal-to-metal contacts return more third harmonic. Using non-linear NLJD for the detection and analysis of the second harmonic of the flooding signals allows identification of explosive devices containing electronic components and third harmonic detection and analysis provides possibilities to find weapons and arms including concealed caches.
Various companies have devices that exploit this technology. For example, I-Vision Systems Technology, Mississauga, Ontario CANADA sells a device, marketed as Military/Law Enforcement Field Non-Linear Junction Detector-ISV-07, which is designed to detect mines and improvised explosive devices within explosive ordinance disposal (E.O.D.) and counter terrorist applications. This device is deployed by bomb squads to detect explosive devices containing electronic components such as: Special remote control; receivers; transceivers; electronic fuses; electronic timers and delayed-action units; engineering mines; and, hidden arms caches.
U.S. Pat. No. 6,057,765, issued to T. H. Jones, et al., entitled “Non-Linear Junction Detector,” discloses a non-linear junction detector designed for counter surveillance measures by using a single circularly polarized antenna to transmit a signal and to receive harmonics of the transmitted signal that are re-radiated by a non-linear junction such as would be found in a eavesdropping device containing a semiconductor. The antenna is mounted on a telescoping antenna extension assembly. A single electrically conductive cable is contained inside the antenna and connects the antenna to the transceiver case which houses the non-linear junction detector electronics. A cable winder is built into the antenna and is employed to provide automatic dispensing and retraction of the cable when the antenna extension assembly is extended or retracted. A display is built into the antenna head assembly to provide signal strength indications and operational information concerning the functioning of the non-linear junction detector to the user of the device. The control signals and power for the display are multiplexed onto the single electrically conductive cable.
U.S. Pat. No. 6,897,777, issued to S. J. Holmes, et al., also entitled, “Non-Linear Junction Detector,” discloses the illumination of a target junction with energy at a fundamental RF frequency. Reflections from the non-linear junction are analyzed to determine the type of junction detected. The power output level of a transmitter emitting the illuminating signal is automatically controlled so as to drive the signal strength of the received signals towards a predetermined value, e.g. a minimum threshold value. An indication of the current received signal strength, adjusted by a factor so as to compensate for any automatic adaptation in the actual transmitter power output level, may be provided to an operator.
Generally, prior art in this field is centered around detection of nonlinear junctions by proximity to the transmit/receive antenna rather than standing off and locating the receiver to be detected in distance and angle measurements. A fixed frequency is used and no effort is taken to take advantage of a threat receiver's antenna and RF front end as an entry point for the transmitted signal used to saturate the receiver to be detected.